This application is related to and claims priority from Japanese Patent Application No. Hei. 10-334390 filed on Nov. 25, 1998, the contents of which are hereby incorporated by reference.
1. Field of the Invention:
The present invention relates to a vehicle air conditioner having a hot-gas bypass function, in which hot-gas refrigerant discharged from a compressor is decompressed and is directly introduced into an evaporator while bypassing a condenser during a heating mode. More particularly, the present invention relates to a control unit which prevents a windshield from being fogged due to vaporization of condensed water on the evaporator when an operation mode of a refrigerant cycle is switched from a cooling mode to the heating mode.
2. Description of Related Art:
In a conventional vehicle air conditioner, hot water (engine-cooling water) is introduced into a heating heat exchanger in winter so that air is heated in the heating heat exchanger using hot water as a heating source. In this case, when temperature of hot water is low, temperature of air blown into a passenger compartment becomes lower and necessary heating capacity is not proposed for the passenger compartment.
To overcome this problem, U.S. Pat. No. 5,291,941 proposes a refrigerant cycle system having a hot-gas bypass function. In the conventional system, when temperature of hot water flowing into a heating heat exchanger is lower than a predetermined temperature, hot-gas refrigerant discharged from a compressor is directly introduced into an evaporator while bypassing a condenser so that air passing through the evaporator is heated by heat radiated from gas refrigerant. That is, in the conventional system, the cooling mode and the heating mode are selectively switched by a single heat exchanger disposed in an air-conditioning case.
However, when an inside air mode is set during the heating mode in winter to prevent polluted outside air from being introduced, air is necessary to be cooled and dehumidified in the evaporator for preventing a windshield of the vehicle from being fogged. Therefore, in this case, the cooling mode may be performed until temperature of outside air is lowered to 0xc2x0 C. On the other hand, the heating mode with hot-gas refrigerant bypassing is generally performed when the temperature of outside air is not higher than 10xc2x0 C. Thus, immediately after the cooling mode is performed at an outside air temperature about 0xc2x0 C. for defogging the windshield, the heating mode with the hot-gas refrigerant bypassing may be need to be switched. In this case, temperature of the evaporator is quickly increased so that condensed water condensed on the evaporator during the cooling mode is evaporated. Therefore, air having a high humidity is blown into the passenger compartment, and the windshield may be fogged again. Further, even when the heating mode is not switched immediately after the cooling mode, when the heating mode with the hot-gas refrigerant bypassing is performed when the condensed water stays on the evaporator, the windshield may be fogged.
On the other hand, in a conventional vehicle air conditioner described in JP-A-6-255341, when a foot mode is selected for heating the passenger compartment, an inside/outside air double layer flow mode is set. During the double layer flow mode, outside air sucked by the first fan is introduced into a first air passage and is blown toward a vehicle windshield and the upper side of the vehicle from a defroster air outlet and a side face air outlet after passing through a refrigerant evaporator as a cooling unit and a refrigerant condenser as a heating unit. On the other hand, inside air sucked from the second fan is blown toward the lower side of the vehicle from a foot air outlet after passing through the refrigerant evaporator and the refrigerant condenser. However, in the conventional air conditioner, the cooling mode and the heating mode of the refrigerant cycle are not switched by a single heat exchanger, and the problem that the windshield is fogged with operation of the heating mode is not described any.
In view of the foregoing problems, it is an object of the present invention to provide a vehicle air conditioner having a refrigerant heat exchanger in which a cooling mode and a heating mode can be switched, while a windshield is prevented from being fogged due to vaporization of condensed water on the refrigerant heat exchanger during the heating mode.
According to the present invention, a vehicle air conditioner includes an air conditioning case for defining an air passage through which air is blown into a passenger compartment, a partition member for partitioning the air passage into a first air passage through which outside air outside the passenger compartment flows into a defroster opening and a second air passage through which inside air inside the passenger compartment flows into a foot opening during a double layer flow mode, a refrigerant cycle through which refrigerant flows, and a control unit. The refrigerant cycle includes a compressor for compressing and discharging refrigerant, a condenser for condensing refrigerant discharged from the compressor during a cooling mode, a first pressreducing unit for decompressing refrigerant from the condenser, a heat exchanger disposed in the air conditioning case for cooling air passing therethrough and for evaporating refrigerant from the first press-reducing unit during the cooling mode, a hot-gas bypass passage through which refrigerant discharged from the compressor is directly introduced into the evaporator while bypassing the condenser and the first press-reducing unit during a heating mode, a second press-reducing unit disposed in the hot-gas bypass passage for decompressing refrigerant discharged from the compressor, and a valve unit for switching a flow direction of refrigerant discharged from the compressor. In the vehicle air conditioner, when the heating mode is set, the double layer flow mode is set. Thus, even when re-evaporation of condensed water on the heater exchanger is generated during the heating mode, vaporized water is mainly blown toward the lower side of the passenger compartment from the foot opening and is hardly blown toward a windshield from the defroster opening, because inside air has a greatly high absolute humidity as compared with outside air. As a result, it can prevent the windshield from being fogged due to vaporization of the condensed water on the heat exchanger.
Further, the double layer flow mode is set when temperature of outside air is lower than a predetermined temperature during the cooling mode. Therefore, even when the heating mode of the refrigerant cycle is selected immediately after the cooling mode of the refrigerant cycle when the temperature of outside air is lower than the predetermined temperature, humidity of air blown toward the windshield is sufficiently restricted.
Preferably, during the cooling mode, the valve unit opens the inlet side of the condenser and closes the inlet side of the hot-gas bypass passage. Further, during the heating mode, the valve unit closes the inlet side of the condenser and opens the inlet side of the hot-gas bypass passage. Thus, the cooling mode and the heating mode of the refrigerant cycle are readily switched in the heat exchanger.